Incidental Synchronous 99mTc-HYNIC-TOC Avid Lesion of the Neck in a Patient with Metastatic Melanoma: A Metastatic Lymph Node or a Carotid Body Tumor Masquerading As a Lymph Node?

A 53-year-old woman with a plantar malignant melanoma lesion was referred to our tertiary clinic for sentinel lymph node mapping. Lymphoscintigraphy with 99mTc-Phytate detected ipsilateral inguinal and popliteal sentinel nodes. After total resection of nodes, the pathology report confirmed that all specimens were involved by the tumor. As part of an institutional study evaluating somatostatin receptor avidity of melanoma by 99mTc-HYNIC-TOC scan, she also underwent a whole-body octreotide scan, which surprisingly showed intense tracer uptake in the right cervical region, confining in SPECT/CT images to a mass at the C2 spinal level, adjacent to the right carotid bifurcation. Neck surgery with gamma probe after injection of another dose of 99mTc-HYNIC-TOC was performed successfully, and the pathology report was consistent with a carotid body tumor. To best our knowledge, our case is the first one in the literature, which reports an incidental paraganglioma with 99mTc-HYNIC-TOC scan which resected via radio-guided surgery, again with 99mTc-HYNIC-TOC tracer.


Introduction
Paragangliomas are rare, slow-growing, and usually benign extra-adrenal neuroendocrine neoplasms of chromaffin-cell origin. Paraganglionic tissues in the carotid body region are called carotid paraganglioma (also known as chemodectoma or carotid body tumor) (1). They can arise from different areas and are named accordingly, such as glomus tympanicum, glomus jugulare, vagal paraganglioma, pulmonary paraganglioma, etc. (1). About 15-35 % of symptomatic cases could be metastatic (2). MRI is the standard imaging modality, but whole-body imaging by 99m Tc-HYNIC-TOC is preferred for patients with risk factors for metastasis (i.e., larger tumors, high mitosis on pathologic study) (3). Best results are acquired using the Ga-68 DOTA-SSA; however, considering its low availability and high cost, a 99m Tc-HYNIC-TOC scan would be an appropriate alternative (4). We present a case of incidental paraganglioma in a patient with melanoma who underwent an experimental 99m Tc-HYNIC-TOC scan.

Case Report
A 53-year-old woman with a left plantar malignant melanoma lesion was referred to our department for sentinel lymph node mapping. Lymphoscintigraphy with 99m Tc-Phytate detected sentinel lymph nodes in popliteal and inguinal regions. After resection of all nodes, a pathologic study confirmed the tumoral involvement of all nodes ( Figure 1).

Figure1. a.
The primary lesion was located in the surface of the right foot. b.

Lymphoscintigraphy images shows sentinel nodes in popliteal and inguinal regions
Then, we performed a 99m Tc-HYNIC-TOC scan to evaluate the tumoral somatostatin receptor avidity as a part of an approved institutional study (IR.MUMS.MEDICAL.REC. 1400.032).
Anterior and posterior whole-body images were obtained with GE healthcare Discovery NM/CT 670 DR dual-headed gamma cameras. The protocol included a 30 to 40minute acquisition (10 cm/min bed reposition) on a 1024×256 matrix with the Low Energy-High Resolution collimators and application of 140 keV peaks with a 15% window, four hours after tracer injection. Whole-body views revealed physiologic biodistribution of radiotracer throughout the body and a focus of intense tracer accumulation in the right side of the neck. Further localization showed a mass in the C2 level on the SPECT/CT images. The lesion was located close to the right common artery bifurcation (Figure2).

Figure2.
Whole body Tc99m-HYNIC-toc scan shows intense uptake in the right cervical region SPECT/CT scan from the neck four hours after tracer injection revealed a 1.5 cm round hypodense lesion with soft tissue density. It was located adjacent to the right common carotid artery bifurcation and showed intense 99m Tc-HYNIC -TOC accumulation. These findings raised suspicion for a metastatic lymph node or a synchronous octreotide-avid neck tumor like a paraganglioma. The SPECT acquisition protocol includes a 30-minute stop and shot acquisition on a 64×64 matrix with the same collimators and peaks as mentioned previously. A Butterworth filter with that an order of 7.0 and a cutoff of 0.30 with attenuation and scatter correction were also used. A low dose CT scan was also performed simultaneously for attenuation correction and better localization of the mentioned lesion (Figure 3). Since lymphatic metastasis to the neck is considered distant metastasis in plantar melanoma, the inguinal and popliteal complete dissections were postponed, and we decided to examine neck mass pathology first. The patient received 10 mCi of intravenous 99m Tc-HYNIC-TOC, two hours before the surgery. During the surgery, we used a gamma probe to precisely localize and remove the mass (Figure 4). Pathological studies confirmed the diagnosis of a carotid body tumor. The patient underwent a complete dissection of inguinal and popliteal nodes in the same week and was referred to the oncology clinic for follow-up.

Discussion
We present an incidental paraganglioma in a patient suffering from melanoma who underwent an experimental 99m Tc-HYNIC -TOC scan. The importance of finding simultaneous melanoma and paraganglioma in a relatively middle-aged person raises suspicion for syndromic diseases; Wadt et al. proposed that mutations in BRCA1-associated protein-1 may make the patient susceptible to melanoma, paraganglioma, and breast cancer. Diagnosis of these patterns, which are usually familial, is vital for future follow-ups of such patients (5). Additionally, even if we consider these situations sporadic, the accurate initial staging of melanoma is crucial to determine the prognosis and management (6). Multiple studies postulated different mechanisms for Peptidetargeted radionuclide therapy (7)(8)(9)(10). Peptidetargeted therapeutic radionuclides, including 177 Lu-DOTA-TATE, are developing methods that are used widely in the treatment of some somatostatin-expressing tumors, namely metastatic neuroendocrine tumors. Still, it warrants further investigation to be applied for metastatic octreotide-avid melanomas.
In conclusion, our case is the first to describe an incidental finding of a paraganglioma by 99m Tc-HYNIC-TOC scan, which was also resected via radio-guided surgery after injection of this tracer. The 99m Tc-HYNIC-TOC scan could be a promising agent for detecting such lesions and associated metastases and radio-guided strategies to decrease surgical interventions and related morbidities.